1. Field of the Invention
The present invention generally relates to digital protective circuit breaker systems. More particularly, this invention relates to addressable control of relay outputs in electrical distribution systems using a network of electronic circuit breakers.
2. Description of the Prior Art
Applications of microprocessors to protective (circuit breaker systems are well known and are becoming increasingly popular for use with electrical power distribution systems. Typically, in such systems, power system data corresponding to pertinent voltages and currents is derived from the power system and converted into corresponding digital values using conventional converters, sample/hold circuits, multiplexers, and analog/digital (A/D) converters. The digitized data or relay inputs are subsequently applied to some form of digital processing device which includes a direct memory access (DMA) controller linked to a data/program memory, and a central processing unit (CPU) where discriminating operations of the respective protective elements are carried out on the basis of the input data supplied thereto and in accordance with predefined programs stored in the system memory.
The use of microprocessors in such systems permits sequential logical processing at high speeds to control the operation of the various relays associated with the protective system by logically combining the results of the discriminating operations and delivering a controlling output to each of the associated circuit breaker elements. The high speed capability of the microprocessors used in such protective systems makes the systems capable of performing discriminating operations for a plurality of protective elements, as well as complicated logical operations.
In electronic circuit breaker systems, trip units and the like using microprocessors are utilized for automatically monitoring line current and related parameters for the presence of predefined conditions such as over-current faults, ground current faults, short circuits, etc. whereupon an associated circuit breaker is "tripped" on the basis of an appropriate output signal generated by the trip unit. Data output from the trip unit generally constitutes trip unit protection, configuration and operating condition information in the form of a continuous uni-directional stream of data which is used for controlling the operational status of the circuit breakers associated with the trip unit.
In addition to controlling the action of circuit breakers, it may be desirable in digital protective systems to control the status of one or more associated relays on the basis of circuit breaker trip information from the trip unit. Such relays may be used to realize a variety of functions such as alarm, display, or programmable functions related to the imminent tripping of a circuit breaker. With conventional trip unit systems for circuit breakers, this type of relay control is difficult and complicated, particularly in "fault-powered" systems where the trip system circuitry draws power from the main line current and, accordingly, a limited amount of time is available for the trip system to perform its functions following detection of a line fault; this is because the resultant tripping of the circuit breaker also removes power to the trip system.
This problem has been approached by the provision of an adapter device in the form of a microcontroller which reads the incoming data stream from a trip unit and clusters, reformats and distributes the information on a multi-drop network based on a multi-drop communications protocol aimed at realizing data exchange without conflicts. Details pertaining to a preferred implementation of such an adapter are disclosed in Haun, et al., U.S. Pat. application Ser. No. 07/585,449, entitled "Communications Arrangement for an Electronic Circuit Breaker Trip System," which is also assigned to the assignee of the present application, Square D Company; the disclosure in that application is incorporated herein by reference.
A major problem associated with conventional trip unit systems is the lack of flexibility with respect to the network parameters of the electrical system being protected which may be used as the basis for controlling the output state of the plurality of relays associated with the system. Even with a system of the above-noted type using a multi-drop network-based adapter, there is a need for efficiently addressing a plurality of relays associated with specific circuit breakers. In addition, an inordinately large number of control lines are required to effectively link the electronic circuit breakers used with the system to the relay controller module in order to realize the necessary relay control. Accordingly, system installation is complicated and system cost is correspondingly increased.
There, accordingly, exists a distinct need for a simple and economical digital protective circuit breaker/relay system providing efficient addressability and increased system flexibility from the user viewpoint by permitting convenient mapping of relay control parameters.